A layman would think: I am installing steam, I want to install steam. What do you mean potentially harmful? Steam ain’t a virus. I have no clue what pop* is and what it does. -> do as I say.
While the prompt is perfectly adequate for those that are technically experienced enough to recognize it is about to uninstall your desktop environment, that isn’t the case for someone who doesn’t know what their desktop environment is. Especially since there is an expectation that installing software does not break things (but, because shared libraries are shared more often than not in Linux, it could!)
I don’t disagree, but the fact is that these people exist (see Linux TT for proof). When things go wrong in Linux, people often end up being directed towards a terminal, even if they shouldn’t be there for plenty of reasons. If you want to be accessible to a layman, largely plug and play is insufficient: it needs to be plug-and-play. I’ve had a wifi dongle not work, I had to compile a kernel module! Those kinds of experiences will cause people that try a flavour of Linux as a desktop os to go elsewhere. Furthermore, I have seen this warning pop up with colleagues when updating software. While they were smart enough to not continue, this stuff does throw up a massive roadblock when it does, especially if you are a layman. If the instructions tell you to install using apt - and this pops up, what would you do? You still want to install the software. It is just a massive source of frustration when something like this happens, even if rare. Doing something sensible (like installing or updating software) should never result in stuff like this popping up.
The moment you need to enter a terminal to fix something - the OS would be irreparably damaged for the average Joe. I would love an immutable distro that would be usable by these people without the risk of harming themselves.